1. Field of the Invention
The present invention generally relates to a double helical gear (or a herringbone gear) of a resin, and a gear train using the same. More specifically, the invention relates to a resin double helical gear which is widely used for various image forming systems, such as copying machines, facsimile terminal equipments and printers, various automotive parts, such as wiper driving units, power window driving units and auto slide door driving units, various electronic equipments, and precision instruments, and a gear train using the same.
2. Description of the Prior Art
A typical ink jet printer serving as an image forming system is often connected to a personal computer to be used, and is arranged on or near a desk, on which the personal computer is operated, to be operated near an operator, so that it is desired to suppress operation noises and vibrations of the ink jet printer.
Therefore, in conventional ink jet printers, a helical gear is used as each of an output gear of a motor and an idle gear meshing with the output gear, and the contact ratio of the output gear to the idle gear is increased to decrease noises (see, e.g., “Handbook of Molded Plastic Gears”, p 22 and p 477, edited by Ad Hoc Committee for Molded Plastic Gear Research of Precision Engineering Institution, published by Sigma Publisher on Apr. 20, 1995). In addition, a spur gear is used as each of a driven gear of a paper feeding roller shaft and an idle gear meshing therewith to prevent thrust force from being applied to the paper feeding roller shaft. Furthermore, if thrust force is applied to the paper feeding roller shaft, a paper feeding transport roller moves so as to be dislocated in the axial directions of the roller shaft. Then, a sheet (a sheet-like recording material, such as a copy paper or a post card) transported by the paper feeding transport roller is transported so as to be dislocated in the axial directions of the paper feeding roller shaft, so that the printing starting position and so forth are deviated to deteriorate the precision of printing.
However, if the helical gears are used as the output gear and the idle gear meshing therewith as conventional ink jet printers, thrust force is applied to both of the gears, so that there are some cases where vibrations are caused by the backlash of the gears and the mounting portion of the rotational shaft rotatably supporting thereon the gears.
Moreover, in the above described ink jet printers, a plurality of idle gears must be arranged between the output gear of the motor and the driven gear of the paper feeding roller shaft, and the number of parts of a gear train is large. Therefore, it is required to reduce the number of the parts in order to reduce the price of the ink jet printers.